Moscow Mule
Vodka, lime and ginger beer. A deliberate 1940s marketing invention that turned out to be a genuinely good drink.
Mai Tai
Two rums, lime, orgeat and curaçao. No pineapple juice, no grenadine, no umbrella required.
Mojito
Rum, lime, mint and soda — built in the glass, and ruined more often by over-muddling than by anything else.
Mint Julep
Bourbon, sugar and mint over a mountain of crushed ice. The cup should frost before you drink it.